Ceramic catalytic converter

ABSTRACT

A pollutant-reducing catalytic converter for an internal combustion engine. The catalytic converter is of ceramic and operates at higher temperatures for increased efficiency. A ceramic foam is used as the substrate for the catalyst. The foam is an open-celled foam and the substrate is deposited on the walls of the cells. Thus, there is a maximum area of catalyst with a minimum amount of catalyst required. The catalytic converter can be placed in the engine compartment adjacent the engine for maximum efficiency without causing temperature problems within the engine compartment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 37 C.F.R. § 1.53(b) of Ser. No.08/844,936 filed Apr. 23, 1997 now U.S. Pat. No. 5,879,640, the entirecontents of which are hereby incorporated by reference, which is a filewrapper continuation of Ser. No. 08/515,850, filed Aug. 16, 1995 nowabandoned.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to methods and apparatus for removing pollutantsfrom the exhaust emissions of internal combustion engines and, moreparticularly, to a high efficiency catalytic converter for removingunburned pollutants from exhaust gases from an internal combustionengine or the like comprising, a catalytic chamber having an inletconnected to receive exhaust gases and an outlet therefrom, thecatalytic chamber having walls of a structural fiber reinforced ceramicmatrix composite (FRCMC) material comprising fibers of a generic fibersystem disposed throughout a pre-ceramic resin in its ceramic state; ahigh temperature resistant, open celled foam disposed within thecatalytic chamber within a path between the inlet and the outlet so thatexhaust gases entering the inlet must pass through a cell path of thefoam to exit through the outlet; and, a catalyst for unburned pollutantsdisposed on walls of cells of the foam.

2. Background Art

For many years, the exhaust systems of automobiles have remainedsubstantially unchanged. There is an exhaust manifold that collects theexhaust gases emitted from the exhaust ports of the engine and outputsthem into an exhaust pipe which conducts the gases to the rear of theautomobile. Typically, a muffler is disposed in-line with the exhaustpipe to muffle the sounds of the gases to an acceptable level. Morerecently, modern exhaust systems have included a catalytic converter tocomplete the oxidation process of unburned particles emitted from theengine, thus reducing pollutants from the exhaust gases. In a typicalprior art exhaust system of such design, the exhaust manifold is boltedor clamped to the engine and the output from the manifold is connectedto an exhaust front pipe which, in turn, is connected to the catalyticconverter.

As depicted in FIGS. 1 and 2, a catalytic converter 10 is nothing morethan a catalyst 12 on a substrate 14. Typically, as depicted in FIG. 1,the substrates 14 are stacked in spaced parallel relationship within ametal container 16 having an inlet 18 and an outlet 20. When hot enough,the catalyst 12 causes unburned pollutants and fuel in the exhaust gases21 passing therethrough to be further oxidized.

Thus, the efficiency of the catalytic converter 10 is directlyproportional to its temperature of operation, the amount of contact areaand the time of contact the exhaust gases 21 have with the catalyst 12.The above described prior art catalytic converter 10 of FIGS. 1 and 2leaves a lot to be desired in that regard. The amount of pollutants andunburned fuel removed from the exhaust gases 21 is a function of theirexposure to the catalyst 12. If there is a large area of contact, ashort time is sufficient. If there is a small area of contact, a longertime of contact is required for all the pollutants and unburned fuel tocontact the catalyst 12. Because of the manner of having the catalyst 12carried by the stacked substrates 14 (or a similar arrangement) thearea-to-volume ratio of the catalyst 12 is not large, the path is notconducive to maximum exposure of the exhaust gases 21 to the catalyst12, and, additionally, the time that the exhaust gases 21 are exposed tothe catalyst 12 is minimal.

Another problem with prior art catalytic converters is that because theyget so hot, they must be placed outside of the engine compartment andunder the vehicle. They are far from the engine itself where they coulddo the most good. Thus, it would be desirable to build the catalyticconverter from a material that could not only withstand the requiredtemperatures; but, in addition, be of an insulating nature so as to beable to contain the high temperatures within the catalytic converter andnot pass them into the surrounding area. In that way, the catalyticconverter could be moved into the engine compartment and closer to theengine without creating engine compartment temperature issues.

Wherefore, it is an object of the present invention to provide acatalytic converter which operates at a very high temperature.

It is another object of the present invention to provide a catalyticconverter which is highly effective in eliminating pollutants fromexhaust gases.

It is still another object of the present invention to provide acatalytic converter which provides a large area of catalyst for contactwith exhaust gases in a minimum volume.

It is yet another object of the present invention to provide a catalyticconverter which can be placed in the engine compartment as close to theengine as possible without creating engine compartment temperatureproblems.

Other objects and benefits of this invention will become apparent fromthe description which follows hereinafter when read in conjunction withthe drawing figures which accompany it.

SUMMARY OF THE DISCLOSURE

The foregoing objects have been achieved by the method of the presentinvention for making a high efficiency catalytic converter for removingunburned hydrocarbon pollutants from exhaust gases from an internalcombustion engine or the like comprising the steps of, forming acatalytic chamber having an inlet connected to receive exhaust gases andan outlet therefrom and further having walls of a structural fiberreinforced ceramic matrix composite material comprising fibers of ageneric fiber system disposed throughout a polymer-derived ceramicresin; disposing a high temperature resistant, open celled foam withinthe catalytic chamber within a path between the inlet and the outlet sothat exhaust gases entering the inlet must pass through a cell path ofthe foam to exit through the outlet; and, depositing a catalyst forunburned hydrocarbon pollutants on walls of cells of the foam.

In the preferred embodiment, the step which includes forming walls of acatalytic chamber of a structural fiber reinforced ceramic matrixcomposite material comprising fibers comprising one or more materialsselected from a generic fiber system disposed throughout a pre-ceramicresin in its ceramic state includes the steps of forming the walls ofreinforcing fibers which can be from alumina, Altex, Nextel 312, Nextel440, Nextel 510, Nextel 550, silicon nitride, silicon carbide, apolysilazane-derived Si-N-C fiber (commonly known as HPZ), graphite,carbon, and peat; saturating the fibers with silicon-carboxyl resin,alumina silicate resin, or monoaluminum phosphate (also known asmonoalumino phosphate) resin; and, firing the fiber-saturated walls at atemperature and for a time which converts the resin into a ceramic.

In one embodiment, the step of disposing a high temperature resistant,open cell ceramic foam within the catalytic chamber comprises the stepof creating an open-celled foam of polymer derived ceramic resin withinthe catalytic chamber.

In another embodiment, that step comprises co-curing the FRCMCstructural shell around a high temperature resistant, open cell ceramicfoam within the catalytic chamber.

In one approach to the step of depositing a catalyst for unburnedhydrocarbon pollutants on walls of cells of the foam, the step comprisesdepositing catalyst on the walls of the cells of the foam by chemicaldeposition.

In another approach, that step comprises the step of using anelectrically-conductive, open-celled ceramic foam; and, the step ofdepositing a catalyst for unburned hydrocarbon pollutants on walls ofcells of the foam comprises, immersing the foam in an electroplatingsolution of the catalyst, connecting the foam as one electrode of anelectroplating system, and electroplating the catalyst on the walls ofthe cells of the foam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified partially cutaway drawing of a prior artcatalytic converter.

FIG. 2 is an enlarged cutaway drawing of the catalytic converter of FIG.1.

FIG. 3 is a simplified partially cutaway drawing of a catalyticconverter according to he present invention in a preferred embodimentthereof.

FIG. 4 is an enlarged cutaway drawing of the catalytic converter of FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In a co-pending application entitled HIGH-EFFICIENCY, LOW-POLLUTIONENGINE by the inventors herein filed on even date herewith and assignedto the common assignee of this application, an improved structural FRCMCmaterial is disclosed having high breakage resistance and particularapplicability to use for parts in a high temperature internal combustionengine. That engine obtains its objectives in large part because of itsability to operate at very high temperatures which result in morecomplete burning of the fuel. Thus, it should emit fewer pollutants inits exhaust gases. To further aid in the reduction of actual pollutantsemitted, a catalytic converter can still be employed to advantage. Thepresent invention is particularly suited for use with that engine totake advantage of the higher temperature exhaust produced thereby.

As depicted in FIG. 3, the catalytic converter 10' of the presentinvention employs a chamber 16' made of the same structural fiberreinforced ceramic matrix composite material so as to be able towithstand the high temperatures. Thus, it is preferred that the chamber16' have walls of a ceramic matrix composite material comprising aceramic matrix having fibers of a generic fiber system disposedthroughout. The preferred FRCMC material employs any of severalpre-ceramic resins commercially available such as Silicon-Carboxyl resin(sold by Allied Signal under the trade name Blackglass, alumina silicateresin (sold by Applied Poleramics under the product designation C02), ormonoaluminum phosphate (also known as monoalumino phosphate) resin,combined with a generic fiber system such as, but not limited to,alumina, Altex, Nextel 312, Nextel 440, Nextel 510, Nextel 550, siliconnitride, silicon carbide, HPZ, graphite, carbon, and peat. To addadditional toughness qualities to the material, the fiber system isfirst coated to 0.1-5.0 microns thickness with an interface materialsuch as Carbon, Silicon Nitride, Silicon Carboxyl, Silicon Carbide orBoron Nitride or a layered combination of one or more of the aboveinterfacial materials. The interface material prevents the resin fromadhering directly to the fibers of the fiber system. Thus, when theresin has converted to a ceramic, there is a slight play between theceramic and fibers imparting the desired qualities to the final fiberreinforced ceramic matrix composite (FRCMC).

To achieve the objective of providing a maximum area of catalyst forcontact with a minimum of catalyst volume employed, the prior artsubstrate is replaced by an open-celled ceramic foam 22 having thecatalyst 12 disposed on the walls of the cells 24 thereof. While anytype of foam capable of withstanding the temperatures involved can beemployed as the foam 22, as depicted in FIG. 4, the multitude of cells24 provide a myriad of paths lined with the catalyst 12 for the exhaustgases 21 to pass through. Thus, the total wetted surface area ofcatalyst 12 is quite large as desired.

The method of manufacture of the catalytic converter 10' of thisinvention is also quite simple as compared with prior art catalyticconverters. The chamber 16' can be made by molding the FRCMC materialand then firing it to convert the resin into a ceramic. If desired, thechamber 16' can then be placed in a protective metal housing or aprotective metal housing can actually be cast around the chamber 16'.

The foam used as the ceramic foam 22 can be any generic ceramic foamsuch as Silicon Carbide foam. Such a foam could either be manufacturedor machined to the inside shape of the catalytic converter 10'. TheFRCMC could be molded around the foam 22 according to techniquesdescribed in the co-pending applications of the inventors herein and thecomponents then cured and fired together prior to catalyst deposition.Silicon Carbide foam is conductive and the catalyst 12 could be appliedby an electroplating process, for example.

In a preferred approach, once the chamber 16' is prepared, the foam 22can be created within the chamber 16' according to techniques describedin co-pending application Ser. No. 08/515,928 filed on Aug. 16, 1995 byDaws et al. entitled CERAMIC FOAM AND METHODS FOR PRODUCING SAME. Thatapplication is assigned to the common assignee of this application andthe teachings thereof are incorporated herein by reference. By so doing,the entire cross sectional area of the path through the chamber 16'between the inlet 18 and the outlet 20 is filled with the foam 22 sothat the exhaust gases 21 must pass through the foam 22 and over thecatalyst 12.

Once the foam 22 is in place, the catalyst can be applied to the wallsof the cells 24 by any of several methods well known to those ofordinary skill in the art such as chemical deposition. It should benoted in this regard that the ceramic foam of the Daws et al.application can be made electrically conductive. Therefore, it should bepossible to apply the catalyst 12 as a very thin layer usingconventional electroplating techniques by placing the chamber 16'containing the foam 22 into an electroplating solution of the catalystand electrically connecting the foam 22 into the system as one electrodethereof.

What is claimed is:
 1. A method of making a high efficiency catalyticconverter for removing unburned hydrocarbon pollutants from exhaustgases from an internal combustion engine, the method comprising thesteps of:a) forming a catalytic chamber having an inlet connected toreceive exhaust gases and an outlet therefrom and further having wallsof an insulative and structural fiber reinforced ceramic matrixcomposite material comprising reinforcing fibers disposed throughout apolymer-derived ceramic resin; b ) disposing a hightemperature-resistant, open-celled foam within the catalytic chamberwithin a path between the inlet and the outlet so that exhaust gasesentering the inlet must pass through a cell path of the foam to exitthrough the outlet; and, c) depositing a catalyst for unburnedhydrocarbon pollutants on walls of cells of the foam.
 2. The method ofclaim 4 wherein said step of forming walls of a catalytic chamber of aninsulative and structural ceramic matrix composite material comprisingreinforcing fibers disposed throughout a polymer-derived ceramic resinfurther comprises:a) forming the walls of fibers of alumina, Nextel 312,Nextel 440, Nextel 510, Nextel 550, silicon nitride, silicon carbide,HPZ, graphite, carbon or peat; b ) saturating the fibers with siliconcarboxyl resin, monoaluminum phosphate resin, or alumina silicate resin;and, c) firing the reinforcing fiber-saturated walls at a sufficienttemperature and for a sufficient length of time such that the resinbecomes a ceramic.
 3. The method of claim 1 wherein said step ofdisposing a high temperature-resistant, open-celled foam within thecatalytic chamber further comprises:forming the open-celled foam ofpolymer-derived ceramic resin within the catalytic chamber.
 4. Themethod of claim 1 wherein said step of depositing a catalyst forunburned hydrocarbon pollutants on walls of cells of the foamcomprises:depositing catalyst on the walls of the cells of the foam bychemical deposition.
 5. The method of claim 1 wherein:a) said step ofdisposing a high temperature-resistant, open-celled foam within thecatalytic chamber further comprises forming an electrically-conductive,open-celled foam of polymer-derived ceramic resin within the catalyticchamber; and, b ) said step of depositing a catalyst for unburnedhydrocarbon pollutants on walls of cells of the foam comprises,b1)immersing the foam in an electroplating solution of the catalyst, b2)connecting the foam as one electrode of an electroplating system; and,b3) electroplating the catalyst on the walls of the cells of the foam.6. A method of making a high efficiency catalytic converter for removingunburned hydrocarbon pollutants from exhaust gases from an internalcombustion engine, the method comprising the steps of:a) forminginsulative and structural walls of a catalytic chamber having an inletconnected to receive exhaust gases and an outlet therefrom ofreinforcing fibers of alumina, Nextel 312, Nextel 440, Nextel 510,Nextel 550, silicon nitride, silicon carbide, HPZ, graphite, carbon orpeat; b ) saturating the reinforcing fibers with silicon carboxyl resin,monoaluminum phosphate resin, or alumina silicate resin; c ) firing thereinforcing fiber-saturated walls at a sufficient temperature and for asufficient length of time such that the resin becomes a ceramic; d )creating a high temperature-resistant, open-celled foam ofpolymer-derived ceramic resin within the catalytic chamber within a pathbetween the inlet and the outlet so that exhaust gases entering theinlet must pass through a cell path of the foam to exit through theoutlet; and, e) depositing a catalyst for unburned hydrocarbonpollutants on walls of cells of the foam.
 7. The method of claim 6wherein said step of depositing a catalyst for unburned hydrocarbonpollutants on walls of cells of the foam further comprises:depositingcatalyst on the walls of the cells of the foam by chemical deposition.8. The method of claim 6 wherein:a) said step of depositing a catalystfor unburned hydrocarbon pollutants on walls of cells of the foamfurther comprises:a1) immersing the foam in an electroplating solutionof the catalyst; a2) connecting the foam as one electrode of anelectroplating system; and, a3) electroplating the catalyst on the wallsof the cells of the foam.